Did TA cars start out as 340 A66 models as 3 of the A66 cars i have looked at have the 5 bolt holes in a half moon pattern to mount the side exhaust pipes where other cars have not also a lot of A66 cars had the rear sway bar & TA spring pack.
I can't answer your specific question Austa, but I can say that both of my 71's one a 383 R/T and the other a 340 car both have those 5 bolt hole patterns on both sides.
Maybe they planned to market the side exit exhaust on other models mate has a 70 383 R/T without the holes i also have a 70 /6 with no holes not that you would have them on a slant 6
